Exhaust gas detection and treatment, and related systems

ABSTRACT

A method for calculating the relative ratios of NH 3  and NO x  in exhaust gases to detect NH 3  slip using NO x  sensors includes measuring a first NO x  level at an upstream NO x  sensor, administering a first predetermined dose of urea to the exhaust gases, measuring a second NO x  level at a downstream NO x  sensor, administering a second predetermined dose of urea to the exhaust gases, measuring a third NO x  level at the downstream NO x  sensor, calculating a difference between the second NO x  level and the third NO x  level, and comparing the difference between the second NO x  level and the third NO x  level to a lookup table to determine a ratio of a concentration of NH 3  to a concentration of NO x  in the exhaust gases. Related systems and methods are also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of the filing date of U. K. PatentApplication 1818633.8, “NOX SLIP DETECTION,” filed Nov. 15, 2018; andU.K. Patent Application 1820820.9, “NH3 SLIP DETECTION IN EXHAUSTSYSTEMS, filed Dec. 19, 2018; the entire disclosures of each of whichare incorporated herein by reference.

FIELD

The present disclosure relates to a method of determining the ratio ofNH₃ to NO_(x) in exhaust gases leaving an exhaust system of an internalcombustion engine.

BACKGROUND

There is a rising demand for cleaner and more efficient internalcombustion engines, especially diesel engines. Diesel engines emitparticulate matter as well as nitrogen oxides (NO_(x)) from theirexhaust systems.

The exhaust systems of working vehicles such as tractors often includeone or more systems to clean the exhaust gases, such as a dieseloxidation catalyst (DOC), a diesel particulate filter (DPF) forparticulate matter treatment, a selective catalytic reduction (SCR),and/or a downstream ammonia oxidation catalyst. A urea solution(CO(NH₂)₂ and water), also known as diesel exhaust fluid (DEF) is oftenused to dose (i.e., treat) exhaust gases, and a chemical reaction in thepresence of catalysts causes a reaction of NO_(x) and NH₃ (ammonia,which is formed by hydrolysis of the urea) to form elemental nitrogen(N₂), water, and carbon dioxide (CO₂).

In general, there is a correlation between the urea dose and NO_(x)reduction efficiency in that a larger dose of urea delivered to theexhaust gas corresponds to a greater the reduction in NO_(x) in thegases released to the atmosphere.

However, under varying engine conditions, unreacted NH₃ can pass or“slip” through the catalytic converter. As such, NH₃ concentration inthe output gases can vary, and detection of the slip is typicallyrequired as part of the system control. Detection of the slip allows theurea to be correctly dosed for the engine operating conditions.Unreacted NH₃ exhausted to the atmosphere may be an environmentalconcern and/or an extra expense that provides no benefit, and therefore,it may be beneficial to limit unreacted NH₃.

It is an object of the present disclosure to provide a method fordetecting NH₃ slip using NO_(x) sensors.

BRIEF SUMMARY

Accordingly, there is provided a method of determining relative ratio ofNO_(x) to NH₃ in exhaust gases, which includes providing an exhaustsystem for an agricultural vehicle, the exhaust system comprising: anupstream NO_(x) sensor; a downstream NO_(x) sensor; a catalyticconverter; a urea injector; and an exhaust control unit. The methodfurther includes measuring a first NO_(x) level at the upstream NO_(x)sensor, administering a first predetermined dose of NH₃ to the exhaustsystem, measuring a second NO_(x) level at the downstream NO_(x) sensor;administering a second predetermined dose of NH₃ to the exhaust system;measuring a third NO_(x) level at the downstream NO_(x) sensor;calculating the difference between the second NO_(x) level and the thirdNO_(x) level; and comparing the difference to a lookup table todetermine the relative ratio of NH₃ and NO_(x).

Advantageously, the second predetermined dose of NH₃ may be larger thanthe first predetermined dose of NH₃. Using a larger dose makes therelative differences of the second and third dose levels easier todetect. Because the normal dosage levels are much smaller, this meansless accurate sensors may be used, which are generally cheaper thanthose that are more accurate.

Advantageously, the exhaust system may include more than one catalyst tofurther reduce NO_(x) levels and therefore improve the chemicalefficiency of the exhaust system.

Advantageously, the catalytic converter may include a selectivecatalytic reduction catalyst. In alternative embodiments, the catalyticconverter may include an ammonia oxidation catalyst.

Advantageously, the exhaust system may further include a temperaturesensor. If the temperature of the exhaust gases is known, the accuracyof estimations and predicted chemical reactions may be improved becausereaction kinetics and equilibrium vary with temperature.

Advantageously, the exhaust system may further comprise a dieselparticulate filter. Including a diesel particulate filter helps reduceparticulate matter that passes to the atmosphere from the internalcombustion engine, reducing pollutants from the exhaust system.

Advantageously, an agricultural vehicle may include an exhaust systemconfigured to carry out the method. An agricultural vehicle includingthe system would be more efficient and have reduced pollutant outputfrom the exhaust system at a lower cost than traditional known methods,such as using NH₃ sensors.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the disclosure will now be described, by way of exampleonly, with reference to the accompanying drawings, in which:

FIG. 1 is a schematic of an exhaust system configured to carry out themethod according to the disclosure;

The drawing is provided by way of reference only, and is not necessarilyto scale.

DETAILED DESCRIPTION

FIG. 1 is a simplified schematic of an exhaust system 10. The exhaustsystem 10 in this particular example is for an agriculture vehicle, suchas a tractor, but may also be used for other exhaust gases (e.g., fromengines in over-the-road vehicles, from stationary sources, etc.). Thearrow X indicates the direction of flow of gases through the exhaustsystem 10, from upstream to downstream. It will be understood thatthroughout the following description, that another source of NH₃ besidesurea (e.g., anhydrous ammonia) may be used.

The exhaust system 10 includes an internal combustion engine 12, acatalytic converter 14, a urea tank 16, a urea injector 18, an upstreamNO_(x) sensor 20, a downstream NO_(x) sensor 22, a temperature sensor24, and an engine control unit 26.

The internal combustion engine 12 in this example is specifically adiesel engine. The internal combustion engine 12 is configured to drivea transmission of the tractor. In alternative embodiments, the internalcombustion engine 12 is configured to drive a generator that produceselectrical power for charging batteries or driving motors. The internalcombustion engine 12 burns diesel fuel with atmospheric air and producespower and waste gases, the waste gases commonly being known as exhaustgases. The exhaust gases are rich in particulates and NO_(x).

The internal combustion engine 12 is in fluid communication with thecatalytic converter 14 via conduit 28 (e.g., an exhaust manifold). Theexhaust gases from the internal combustion engine 12 exit the internalcombustion engine 12 at A, pass via conduit 28 and enter the catalyticconverter 14 at B. The conduit 28 between the internal combustion engine12 and the catalytic converter 14 may be formed by any suitable means,for example a tube or conventional exhaust pipe constructed from mildsteel or stainless steel. In some embodiments, the conduit 28 may beceramic-coated to provide better thermodynamic (e.g., insulative)properties.

The catalytic converter 14 may include one or more catalysts, such as aselective catalytic reduction catalyst, a diesel oxidation catalyst, anammonia oxidation catalyst, or a hybrid of different catalyst types.

Exhaust gases exit the catalytic converter 14 at C and enter anotherconduit 30, which may be referred to in the art as a tail pipe or stack.The exhaust gases exit the conduit 30 at D, which may be open to theatmosphere. The conduit 30 may be of any conventional design.

The urea tank 16 is provided as a reservoir for urea (as a source of NH₃for reduction of NO_(x)). The urea is used as a dosing agent for theexhaust system 10. The urea tank 16 is in fluid communication with theurea injector 18 via line 32.

The urea injector 18 is of suitable type and is provided to dose theexhaust gases in the exhaust system 10 with urea from the urea tank 16.In this example, the urea injector 18 is provided in the conduit 28between A and B such that urea may be administered to the exhaust gasesprior to their entering the catalytic converter 14.

The upstream NO_(x) sensor 20 is provided in the conduit 28 upstream ofthe urea injector 18 and is configured to provide measurements of theNO_(x) levels in the exhaust gases leaving the internal combustionengine 12.

The downstream NO_(x) sensor 22 is provided in the conduit 30 between Cand D. The downstream NO_(x) 22 sensor is thus situated downstream ofthe catalytic converter 14, the urea injector 18, and the upstreamNO_(x) sensor 20. The downstream NO_(x) sensor 22 is configured tomeasure the levels of NO_(x) in exhaust gases in the conduit 30, i.e.downstream of the catalytic converter 14.

The temperature sensor 24 in this example is situated in the conduit 28between A and B. The temperature sensor 24 is also situated between theurea injector 18 and the catalytic converter 14. In other examples, thetemperature sensor 24 may be omitted. The temperature sensor 24 is ofany suitable type, such as a thermocouple. The temperature sensor 24 isconfigured to measure the temperature of exhaust gases flowing in theconduit 28. That is, the temperature sensor 24 is used to measure thetemperature of exhaust gases as they exit the internal combustion engine12 and before they enter the catalytic converter 14. In alternativeembodiments, it will be understood that the temperature sensor 24 may beupstream of the urea injector 18 and/or further temperature sensors maybe positioned throughout the exhaust system 10.

The engine control unit (ECU) 26 is provided as part of the exhaustsystem 10. However, it will be understood that the engine control unit26 may be a main or auxiliary control unit provided as a standalonecontrol unit on a vehicle or in data communication with another controlunit on the vehicle.

In this specific example, the engine control unit 26 is a main enginecontrol unit for the vehicle and is configured to receive measurementsfrom vehicle sensors and send messages to various vehicle components anddevices.

The engine control unit 26 is in data communication with each of theinternal combustion engine 12, the urea injector 18, the upstream NO_(x)sensor 20, the downstream NO_(x) sensor 22, and the temperature sensor24.

When the exhaust system 10 is in use, exhaust gases containing NO_(x)are expelled from the internal combustion engine 12 and are vented tothe atmosphere at D after passing through the catalytic converter 14.

To reduce the NO_(x) content in the exhaust gases, the exhaust gases aredosed with urea (which is hydrolyzed to form NH₃) at the urea injector18 before entering the catalytic converter 14. This process is referredto in the art as Selective Catalytic Reduction (SCR), is well known inthe art, and is not described in detail herein.

During the SCR process, the NH₃ formed from the dosed urea is notnecessarily entirely consumed by reacting with the NO_(x).

It is useful to know the ratio of NO_(x) to NH₃ in the exhaust gases atD so that the urea dosing, operating temperature, or other parametersmay be adjusted to improve the removal of NO_(x) and/or particulatematter from the exhaust gases.

It is possible to include a further sensor configured to measure NH₃concentration into the system in the conduit 30 between C and D.Combined with the data measured from the downstream NO_(x) sensor 22, itwould then be possible to calculate the ratio of NO_(x) and NH₃ in theexhaust gases leaving the exhaust system 10.

Disadvantageously, the addition of a sensor to directly measure thelevels of NH₃ in the exhaust gases increases the system cost andcomplexity. Instead, the NO_(x) sensors 20, 22 provided in the exhaustsystem 10 shown may be used to calculate the relative ratios of NO_(x)and NH₃ in the exhaust gases without measuring the concentration of NH₃,as described below.

To calculate the relative ratios of NO_(x) and NH₃ in the exhaust gaseswhen the exhaust system 10 is in use, a baseline concentration of NO_(x)(i.e., a first NO_(x) level) is measured by the upstream NO_(x) sensor20 and communicated to the ECU 26. The exhaust gases are dosed with aknown quantity (i.e., a first predetermined dose) of urea (NH₃ source)at the urea injector 18, which is downstream of the upstream NO_(x)sensor 20 (and therefore, the injection of urea does not perturb thefirst NO_(x) level at the upstream NO_(x) sensor 20). The exhaust gases,now enriched with NH₃, pass into the catalytic converter 14. In thecatalytic converter 14, a chemical reduction reaction takes place,whereby the NH₃ reacts with the NO_(x) to convert some of the NO_(x) toH₂O (water), N₂ (nitrogen gas), and optionally CO₂ (carbon dioxide).However, the NO_(x) and NH₃ do not necessarily entirely react, and assuch the exhaust gases exiting the catalytic converter 14 at C maycontain H₂O, O₂, N₂, NH₃, and NO_(x), among other gases and particles.The concentration of NO_(x) (i.e., a second NO_(x) level) is measured bythe downstream NO_(x) sensor 22.

The preceding process occurs continually when the exhaust system is inuse and when NO_(x) reduction is required. The reaction in the catalyticconverter 14 generally produces stable results and conversion ratios,and thus, the second NO_(x) level measured by the downstream NO_(x)sensor 22 is generally stable.

To calculate the relative ratios of NH₃ the NO_(x) and thereby checkthat the process is running correctly, the dose of urea applied to theexhaust gases at the urea injector 18 is spiked to a secondpredetermined dose for a period of time. That is, the dosing of urea isnormally stable and relative to the measured NO_(x) levels and isapplied at a first predetermined level, which is appropriate to themeasured NO_(x) levels at the upstream NO_(x) sensor 20, and is setaccording to a predetermined dosing map. The second predetermined doseor spiked level is significantly higher than what would be requiredaccording to the aforementioned dosing map. The NO_(x) concentrationfollowing the spike is measured in the exhaust gases in the conduit 30by the downstream NO_(x) sensor 22 (i.e., a third NO_(x) level).

The difference between the second and third NO_(x) levels can becomputed by the engine control unit 26 and compared to a stored map ortable to determine the relative ratio of NH₃ and NO_(x). The stored mapis typically constructed from results acquired from testing (i.e.,calibration).

The temperature sensor 24 can be used to provide further data and moreprecisely estimate the amount of urea to apply because reaction kineticsand equilibrium vary with temperature.

In alternative embodiments, a further catalyst may be provided in theexhaust system 10. In a specific embodiment, this further catalyst is aDOC catalyst and is positioned upstream of the upstream NO_(x) sensor20.

In further alternative embodiments, the upstream NO_(x) sensor 20 ispositioned anywhere in the exhaust system 10 upstream of the ureainjector 18.

Furthermore the exhaust system 10 may include a diesel particulatefilter. This diesel particulate filter may for instance be situateddownstream of the catalytic converter 14.

The disclosure is not limited to the embodiments or examples describedherein, and may be modified or adapted without departing from the scopeof the present disclosure.

1. A method of determining a ratio of NO_(x) to NH₃ in exhaust gases,the method comprising: providing an exhaust system for an agriculturalvehicle, the exhaust system comprising: an upstream NO_(x) sensor; adownstream NO_(x) sensor; a catalytic converter comprising a firstcatalyst; a urea injector; and an exhaust control unit; measuring afirst NO_(x) level of the exhaust gases at the upstream NO_(x) sensor;administering a first predetermined dose of urea to the exhaust gases;measuring a second NO_(x) level of the exhaust gases at the downstreamNO_(x) sensor; administering a second predetermined dose of urea to theexhaust gases; measuring a third NO_(x) level of the exhaust gases atthe downstream NO_(x) sensor; calculating a difference between thesecond NO_(x) level and the third NO_(x) level; and comparing thedifference between the second NO_(x) level and the third NO_(x) level toa lookup table to determine a ratio of a concentration of NH₃ to aconcentration of NO_(x) leaving the exhaust gases.
 2. The method ofclaim 1, wherein the second predetermined dose of urea is larger thanthe first predetermined dose of urea.
 3. The method of claim 1, whereinthe exhaust system further comprises a second catalyst.
 4. The method ofclaim 1, wherein the first catalyst is a selective catalytic reductioncatalyst.
 5. The method of claim 3, wherein the first catalyst is anammonia oxidation catalyst.
 6. The method of claim 1, wherein theexhaust system further comprises a temperature sensor.
 7. The method ofclaim 1, wherein the exhaust system further comprises a dieselparticulate filter.
 8. An agricultural vehicle comprising an exhaustsystem configured to carry out the method of claim
 1. 9. A method oftreating an exhaust gas, the method comprising: measuring a first NO_(x)concentration in an exhaust gas flow; administering a first dose of NH₃to the exhaust gas flow during a first time period and passing theexhaust gas flow through a catalytic converter; measuring a secondNO_(x) concentration in the exhaust gas downstream of the catalyticconverter responsive to the first dose; administering a second dose ofNH₃ to the exhaust gas flow during a second time period and passing theexhaust gas flow through the catalytic converter; measuring a thirdNO_(x) concentration in the exhaust gas downstream of the catalyticconverter responsive to the second dose; calculating a differencebetween the second NO_(x) concentration and the third NO_(x)concentration; and comparing the difference between the second NO_(x)concentration and the third NO_(x) concentration to calibration data todetermine a ratio of a concentration of NH₃ to a concentration of NO_(x)in the exhaust gas flow leaving the catalytic converter.
 10. The methodof claim 9, wherein the second dose of NH₃ is larger than the first doseof NH₃.
 11. The method of claim 9, further comprising filteringparticulate material from the exhaust gas flow.
 12. The method of claim9, wherein administering the first dose of NH₃ and administering thesecond dose of NH₃ each comprise injecting urea into the exhaust gasflow and hydrolyzing urea to form NH₃ and CO₂.
 13. The method of claim9, further comprising reacting the NH₃ with NO_(x) in the catalyticconverter to form N₂ and H₂O.
 14. The method of claim 9, furthercomprising determining the ratio of the concentration of NH₃ to theconcentration of NO_(x) in the exhaust gas flow without measuring theconcentration of NH₃.
 15. An exhaust gas treatment system, comprising:an upstream NO_(x) sensor; a urea injector; a catalytic convertercomprising a first catalyst downstream of the upstream NO_(x) sensor andthe urea injector; a downstream NO_(x) sensor downstream of thecatalytic converter; and an exhaust control unit, wherein the exhaustcontrol unit is configured to: measure a first NO_(x) concentration inan exhaust gas flow at the upstream NO_(x) sensor; administer a firstdose of urea to the exhaust gas flow at the urea injector; measure asecond NO_(x) concentration in the exhaust gas at the downstream NO_(x)sensor; administer a second dose of urea to the exhaust gas flow at theurea injector; measure a third NO_(x) concentration in the exhaust gasat the downstream NO_(x) sensor; calculate a difference between thesecond NO_(x) concentration and the third NO_(x) concentration; andcompare the difference between the second NO_(x) concentration and thethird NO_(x) concentration to calibration data to determine a ratio of aconcentration of NH₃ to a concentration of NO_(x) in the exhaust gasflow entering the exhaust system.
 16. The system of claim 15, whereinthe catalytic converter further comprises a second catalyst having acomposition different from the first catalyst.
 17. The system of claim15, wherein the first catalyst is a selective catalytic reductioncatalyst.
 18. The system of claim 17, wherein the first catalyst is anammonia oxidation catalyst.
 19. The system of claim 15, furthercomprising a temperature sensor configured to communicate with theexhaust control unit.
 20. The system of claim 15, further comprising adiesel particulate filter.